GNU bug report logs - #57801
'inferior-with-channels' is eager, making it hard to use in channels

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Maxime Devos <maximedevos <at> telenet.be>
To: bug-guix <bug-guix <at> gnu.org>
Subject: 'inferior-with-channels' is eager, making it hard to use in channels
Date: Wed, 14 Sep 2022 14:28:20 +0200

[Message part 1 (text/plain, inline)]

As experienced by Luks6655, you can't do

(define inferior (inferior-with-channels CHANNELS))

on the top-level of a channel module.  I think the issue is that 
inferior-with-channels is eager (not lazy), so it cannot be used in a 
channel on the top-level, as builds (including channel builds) are 
isolated from the network and have limited access to the file system.

If it would be made lazy, then

(define inferior (inferior-with-channels CHANNELS))
(define-public p
  (package
    [...]
    (inputs (list (lookup-inferior-package inferior "hello")))))

should, in theory, work (unverified).

Greetings,
Maxime.

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Message #8 received at 57801 <at> debbugs.gnu.org (full text, mbox):

From: Lukasz Olszewski <dev <at> lukaszolszewski.info>
To: 57801 <at> debbugs.gnu.org
Subject: Re: 'inferior-with-channels' is eager,
 making it hard to use in channels
Date: Wed, 14 Sep 2022 19:18:03 +0200

Additionally this fails even when used like this:

(define inferior
  (mlambda ()
    (inferior-for-channels channels)))

(lookup-inferior-packages (inferior) "somepackage")

Message #11 received at 57801 <at> debbugs.gnu.org (full text, mbox):

From: Maxime Devos <maximedevos <at> telenet.be>
To: Lukasz Olszewski <dev <at> lukaszolszewski.info>, 57801 <at> debbugs.gnu.org
Subject: Re: bug#57801: 'inferior-with-channels' is eager, making it hard to
 use in channels
Date: Thu, 15 Sep 2022 17:46:15 +0200

[Message part 1 (text/plain, inline)]

On 14-09-2022 19:18, Lukasz Olszewski wrote:
> Additionally this fails even when used like this:
> 
> (define inferior
>    (mlambda ()
>      (inferior-for-channels channels)))

This makes it lazy (not eager).

> (lookup-inferior-packages (inferior) "somepackage")

You are running (inferior) directly after defining the lazy thing, 
making it effectively _eager_ (not lazy) again.

Instead of doing this on the top-level, move the 
lookup-inferior-packages to inside the 'inputs' or 'native-inputs', to 
_keep_ it lazy.

Greetings,
Maxime.

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